Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 7, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2017/07/009
Keywords
modified gravity; cosmological perturbation theory; dark matter theory
Funding
- MEXT-Program for the Strategic Research Foundation at Private Universities
- JSPS Research Fellowships for Young Scientists [15J04044]
- JSPS [16H01102, 16K17707]
- Grants-in-Aid for Scientific Research [16K17707, 17J04865, 17H06357, 16H01102, 15J04044] Funding Source: KAKEN
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We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher derivative terms suffers from gradient instabilities in scalar perturbations. To seek for an instability-free extension of imperfect dark matter, we develop an effective theory of cosmological perturbations subject to the constraint on the scalar field's kinetic term. This is done by using the unifying framework of general scalar-tensor theories based on the ADM formalism. We demonstrate that it is indeed possible to construct a model of imperfect dark matter which is free from ghost and gradient instabilities. As a side remark, we also show that mimetic F(R) theory is plagued with the Ostrogradsky instability.
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